Temporal comparisons in bacterial chemotaxis

Segall, Jeffrey E. and Block, Steven M. and Berg, Howard C.
(1986)
Temporal comparisons in bacterial chemotaxis.
Proceedings of the National Academy of Sciences of the United States of America, 83
(23).
pp. 8987-8991.
ISSN 0027-8424.
http://resolver.caltech.edu/CaltechAUTHORS:SEGpnas86

Abstract

Responses of tethered cells of Escherichia coli to impulse, step, exponential-ramp or exponentiated sine-wave stimuli are internally consistent, provided that allowance is made for the nonlinear effect of thresholds. This result confirms that wild-type cells exposed to stimuli in the physiological range make short-term temporal comparisons extending 4 sec into the past: the past second is given a positive weighting, the previous 3 sec are given a negative weighting, and the cells respond to the difference. cheRcheB mutants (defective in methylation and demethylation) weight the past second in a manner similar to the wild type, but they do not make short-term temporal comparisons. When exposed to small steps delivered iontophoretically, they fail to adapt over periods of up to 12 sec; when exposed to longer steps in a flow cell, they partially adapt, but with a decay time of >30 sec. cheZ mutants use a weighting that extends at least 40 sec into the past. The gain of the chemotactic system is large: the change in occupancy of the receptor molecule produces a significant response.